The following relates to the electrical power arts. It particularly relates to monitoring a safe electrical disconnection of a high voltage circuit for servicing, and will be described with particular reference thereto. However, the following will also find application in routine monitoring of electrical line voltages and in other aspects of electrical safety.
To ensure safety during servicing of electrical systems and circuits which carry high voltages, a xe2x80x9clockout/tagoutxe2x80x9d procedure is typically followed. A circuit breaker or ON/OFF switch that delivers power to the circuit to be serviced is opened or disengaged to disconnect electrical power from the circuit, and the breaker is physically locked into the opened or disengaged position using a padlock or other device (the xe2x80x9clockoutxe2x80x9d). Additionally, the servicing technician affixes a tag to the physically locked breaker that provides information such as the technician""s identity and contact information, service authorization information, and the like (the xe2x80x9ctagoutxe2x80x9d). The tag typically is bright red or otherwise prominently displayed, and includes a plain language warning that only the installing technician is authorized to remove the lockout/tagout and reenergize the circuit.
The lockout/tagout procedure greatly reduces the possibility of human error causing inadvertent application of power to the circuit under service. However, safety can be compromised even when the lockout/tagout procedure is properly followed, due to various potential sources of dangerously high voltages in the isolated circuit. For example, potential unexpected sources of d.c. energy include line capacitance, bypass capacitors, or power factor correction banks. Potential unexpected sources of a.c. energy include standby power generators, motor back-EMF, or human operation of an associated switch. Moreover, power ON/OFF switches or circuit breakers are not immune to failure, and the locked out breaker could potentially still be transmitting power.
Recognizing that the most dangerous power panel or box can be the one believed to be at zero energy potential, the Occupational Safety and Health Administration (OSHA) has issued regulation OSHA 1910.147 entitled xe2x80x9cControl of Hazardous Energy (Lockout/Tagout)xe2x80x9d which includes identification of residual or stored energy as a hazard. OSHA 1910.147 requires that electrical isolation be verified after lockout/tagout. Furthermore, it requires that the verification of isolation continue throughout the electrical servicing if there is a possibility of reaccumulation of hazardous levels of stored energy.
In the past, electrical meters, neon indicators, or incandescent light bulbs have been used to verify electrical isolation. However, these devices have a number of problems. One problem is a limited operating range. Hazardous energy potentials begin in the vicinity of 30 volts to 40 volts. A commercial three-phase line supply can be as high as 460 vac line-to-line in the United States, and up to 600 vac in Canada. A simple rectifier on a 600 vac line could produce an 848 vdc potential. Past neon indicators and incandescent bulbs do not operate over such a wide range of potential stored voltages.
Additionally, these indicators do not provide information about the hazard. There is no indication of the type of stored energy potential (a.c. or d.c.) or the polarity in the case of a d.c. potential. Such information can be useful for identifying and eliminating the source.
Another problem with these indicators is inconvenience. Typically, the technician inserts the indicator between each of the various line combinations. For a three-phase circuit there are three lines (four including a neutral in a xe2x80x9cwyexe2x80x9d configuration) plus a circuit ground, and so a large number of combinations should be tested. Manual testing of these various combinations provides many opportunities for the servicing technician to inadvertently miss a test.
Yet another problem with past indicators is that they do not provide a continuous and intuitive visual indication of potential hazards. These devices are typically not configurable to provide continuous monitoring of all possible line combinations throughout servicing, as required for compliance with OSHA 1910.147.
Still yet another problem with past indicators is that the electrical panel is opened to provide access for the testing. This provides an opportunity for contact by the technician or others with any hazardous voltages contained therein.
The following contemplates an improved apparatus and method that overcomes the aforementioned limitations and others.
According to one aspect, an electrical safety monitor is disclosed for monitoring electrical energy potentials of electrical lines of an electrical panel. A housing includes a display face and a securing section that connects with the electrical panel. Electrical circuitry is contained in the housing. The electrical circuitry communicates with the electrical lines, and defines high impedance electrical paths between pairs of electrical lines of the electrical panel. Each high impedance path includes a positive light emitting diode arranged to draw current from a line carrying a positive electrical energy potential and a negative light emitting diode arranged to draw current from a line carrying a negative electrical energy potential relative to the positive electrical energy potential. The positive and negative light emitting diodes are disposed on the display face of the housing. Each light emitting diode produces light responsive to current flow in a high impedance path that includes the light emitting diode.
According to another aspect, an electrical safety monitor is disclosed for monitoring electrical energy potentials of electrical lines. A plurality of solid-state light-emitting devices are disposed in a human-viewable arrangement. Each light emitting device electrically communicates with a selected electrical line and produces a light output indicative of an electrical energy potential between the selected electrical line and at least one other line.
According to yet another aspect, a method is provided for providing warning of a hazardous electrical voltage on a circuit. High impedance rectifying paths are arranged between electrical lines of the circuit. The high impedance rectifying paths include light emitting diodes. Each light emitting diode produces light responsive to a current flowing in a high impedance rectifying path that includes the light emitting diode. A display that includes the light emitting diodes is monitored to detect a hazardous electrical voltage.
One advantage resides in providing monitoring over a wide range of stored electrical energy potentials, from the lowest hazardous levels of about 30 volts to 40 volts up to at least about a kilovolt.
Another advantage resides in providing a convenient visual indication of a detected stored electrical potential level and type (a.c. or d.c.), as well as polarity information for d.c. potentials.
Another advantage resides in simultaneous automatic testing of all line combinations in a three-phase line supply, including line potentials respective to ground.
Yet another advantage resides in providing a continuous and intuitive visual indication of potential stored electrical energy hazards for every line combination in a three-phase line supply throughout the servicing process.
Still yet another advantage resides in providing verification of electrical circuit isolation without opening or otherwise accessing the electrical panel.
Numerous additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments.